American Express will enable its credit cards to work with the Isis Mobile Wallet system once the technology is deployed in Salt Lake City and Austin this summer, Isis announced Thursday.

American Express joins Chase, Capital One and Barclaycard in the Isis initiative; the other companies announced their support earlier this year. Amex will allow its consumer credit card and other cards to be part of Isis Mobile Wallet.

Smartphone owners who use devices equipped with Near Field Communication (NFC) chips and who have downloaded the Isis mobile payment app will be able to tap their phones on NFC readers at stores to make purchases. Many mobile wallet applications also require inputting a PIN before the transfer is completed for added security.

NFC phones are widely used in South Korea, Japan and parts of China to pay transit fares and make small retail purchases. Analysts say the technology hasn't caught on in many regions, including the U.S., because of a shortage of NFC-ready phones and NFC-ready payment terminals, and because few wireless carriers, credit service providers and banks have entered into the necessary cooperative agreements. The weak economy has also been cited as a reason for the slow growth.

Isis is a joint venture between AT&T, T-Mobile USA and Verizon Wireless, but the mobile commerce network that Isis is building will be open to all merchants, banks, payment networks and wireless carriers, Isis said.

Google's mobile payment system, Google Wallet, first deployed in the Nexus S smartphone sold by Sprint last September, but it has been slow to catch on. Sprint is now also selling the Galaxy Nexus, including an unlocked version, with the Google Wallet application installed. Google has also worked with various retailers to offer mobile coupons via NFC a to encourage people to use the technology.

Amex's Isis announcement follows MasterCard's announcement Monday of PayPass Wallet Services, a digital wallet that is open to third parties to create payment systems under their own brands. PayPass can be used with NFC-ready phones for tap-to-pay purchases or for phone or Web transactions.

Along with Google and MasterCard, Visa, PayPal and other financial services companies also have digital wallet systems.

Isis officials haven't specified which smartphones will work with the Isis Mobile Wallet, nor have they given a date for the launch of the service in Salt Lake or Austin. They have only said that the launches will occur this summer.